Although this invention will be described for the purpose of providing a working platform for welders working on "stove-pipe" joints of a marine pipeline being assembled on the deck of a barge, the invention will find applications other than for assembling a pipeline. Such stove-pipe joints are simultaneously made on an assembly-line basis using several welding stations. After the last joint is completed, the barge is pulled forward under the pipeline. Oscillatory relative motion between the pipeline and the barge is common, chiefly due to wave-induced motions of the barge. Pipe treating equipment, such as pipe-support rollers and tensioners, normally limit the motion range of the pipeline to be mostly parallel to the deck and in an axial direction of the pipeline.
When workers attempt to perform some task on the pipeline, they must contend with and adapt themselves to the relative motion above described. Such adaptation results in the workers becoming distracted and fatigued. When such relative motions become intense, there is even good reason to fear for the safety of the workers, since they may trip over cables and other obstacles normally found on the base. Welders are particularly vulnerable, since their face masks inhibit their vision, except in the direction of the weld.
It is an object of this invention to selectively couple a rollable scaffold to a pipeline. When not coupled to the pipeline, the scaffold rests on the usual working surface. The coupling is effected by a fluid-operated system which is reliable, inexpensive, and safe. Because the amount of space, in which relative motion can take place between the pipeline and the working surface, is limited, the fluid-operated system incorporates scaffold motion limiting means. The system is automatically reactivated after the scaffold moves away from a motion-limiting means. The means attaching the scaffold to the pipeline permit the development of static frictional forces having a resultant which causes the scaffold to move compliantly with the pipeline. An advantage of such attachment means is that when the scaffold strikes some rigid object, slippage between the attachment means and the pipe can occur without causing damage to the pipe. Various attachment means can be provided. For example, multiple opposed clamps can grasp the pipe between them. The preferred attachment means is controlled by jacking between the scaffold and the pipe.